1. Field of the Invention
The present invention relates to a compressor and, more particularly, to an apparatus and method for controlling an operation of a reciprocating compressor.
2. Description of the Conventional Art
In general, without a crank shaft for converting a rotational motion to a linear motion, a reciprocating compressor has a little friction loss, and thus, it has higher compression efficiency than general compressors.
When the reciprocating compressor is used for a refrigerator or an air-conditioner, a compression ratio of the reciprocating compressor can be varied to control cooling capacity by varying a stroke voltage applied to the reciprocating compressor.
The conventional reciprocating compressor will now be described with reference to FIG. 1.
FIG. 1 is a block diagram showing the construction of an apparatus for controlling an operation of a reciprocating compressor in accordance with a conventional art.
As shown in FIG. 1, the apparatus for controlling an operation of the reciprocating compressor includes: a voltage detector 14 for detecting a voltage applied to a reciprocating compressor 13 as a stroke of the reciprocating compressor 13 is varied; a current detector 12 for detecting a current applied to the reciprocating compressor 13 as the stroke is varied; a microcomputer 15 for calculating a stroke based on the voltage value detected by the voltage detector 14 and the current value detected by the current detector 12, comparing the calculated stroke with a stroke reference value, and generating a switching control signal according to the comparison result; and a power supply unit 11 for supplying a stroke voltage to the reciprocating compressor 13 by controlling ON/OFF of AC power supplied to the reciprocating compressor 13 with an internal triac Tr1 according to the switching control signal generated by the microcomputer 15. Herein, the reciprocating compressor 13 varies the stroke upon receiving the stroke voltage provided to an internal motor (not shown) according to the stroke reference value previously set by a user, and reciprocally moves an internal piston (not shown).
The apparatus for controlling an operation of the reciprocating compressor in accordance with the conventional art operates as follows.
First, when a voltage is supplied to the internal motor according to the stroke reference value as set by the user, the reciprocating compressor 13 varies the stroke and reciprocally moves the piston. Herein, the stroke means a distance along which the piston of the reciprocating compressor 13 is reciprocally moved.
The turn-on duration of the triac (Tr1) of the power supply unit 11 is lengthened by the switching control signal outputted from the microcomputer 15, and accordingly, the AC power is supplied to the reciprocating compressor 13 to drive the reciprocating compressor 13. At this time, the voltage detector 14 and the current detector 12 detect the voltage and the current applied to the reciprocating compressor 13, respectively, and output the detected voltage and current values to the microcomputer 15.
The microcomputer 15 calculates the stroke of the reciprocating compressor 13 based on the voltage and current values respectively detected by the voltage detector 14 and the current detector 12, compares the calculated stroke value with the stroke reference value, and generates a switching control signal according to the comparison result. For example, if the calculated stroke value is smaller than the stroke reference value, the microcomputer 15 outputs a switching control signal for lengthening the turn-on duration of the triac (Tr1) to the power supply unit 11 to increase the stroke voltage supplied to the reciprocating compressor 13.
If, however, the calculated stroke value is greater than the stroke reference value, the microcomputer 15 outputs a switching control signal for shortening the turn-on duration of the triac Tr1 to the power supply unit 11 to reduce the stroke voltage supplied to the reciprocating compressor 13.
The single capacitor 16 connected in series to the internal motor of the reciprocating compressor 13 countervails an inductance of a coil wound in the internal motor.
Meanwhile, in the conventional apparatus for controlling an operation of the reciprocating compressor, when the voltage is applied to the motor of the compressor 13 through the triac Tr1 in order to control the stroke of the compressor, a noise is generated. In order to cancel the noise, a relay 17 and a motor 18 consisting of a main coil 19 and a sub-coil 20 as shown in FIG. 2 are required.
For example, the relay selects only the main coil 19 or both the main coil 19 and the sub-coil 20 according to a change in the voltage inputted to the compressor and a change in an operation load of the compressor, to thereby vary capacity of the motor 18. For example, if an inputted voltage is increased or an operation load of the compressor is greater than a pre-set reference load (namely, in case of an overload), the microcomputer 15 controls the relay 17 to select only the main coil 19 to reduce a back electromotive force constant of the motor 18.
Meanwhile, if the voltage inputted to the compressor is reduced or the operation load of the compressor is smaller than the pre-set reference load (namely, underload), the microcomputer 15 controls the relay 17 to select both the main coil 19 and the sub-coil 20 to increase the back electromotive force constant of the motor 18. Herein, the operation mode of the compressor is changed to a power mode or a safe mode according to the change in the voltage inputted to the compressor and the change in the operation load of the compressor. The power mode refers to a method in which the motor is operated through only the main coil while the safe mode refers to a mode in which the motor is operated through both the main coil and the sub-coil.
The number (N) of times of winding of the coil wound at the motor 18 of the reciprocating compressor is proportional to the back electromotive force constant of the motor, so when a certain voltage is applied to the compressor, the stroke of the compressor and the number of times of winding of the coil are in inverse proportion as expressed in equation (1) shown below:
                    Stroke        ≅                  Voltage          MotorConstant                ∝                  Voltage          N                                    (        1        )            
Accordingly, the motor can be controlled by varying its capacity by controlling the relay 17 according to the change in power applied to the compressor and the change in the operation load of the compressor.
However, as for the apparatus for controlling the operation of the reciprocating compressor in accordance with the conventional art, when the compressor is in the power mode or in the safe mode, power is applied to the motor 18 of the compressor through only one capacitor connected to the motor 18, causing a problem that the operation of the compressor is unstable. For example, when the operation mode of the compressor is changed from the safe mode to the power mode or from the safe mode to the power mode, the number of times of winding of the coil of the motor is changed and thus the inductance of the motor coil is changed. But since the compressor is operated through only one capacitor, the compressor is operated unstably.
U.S. Pat. No. 6,644,943 issued on Nov. 11, 2003 also discloses a reciprocating compressor.